Sometimes it is impractical to run electrical cable behind a wall when installing new receptacles. That necessitates finding an unobtrusive way to run the wires from the existing power supply to the new outlets. Usually this can be accomplished by simply threading the wires behind skirting boards and, if necessary, behind the casing of a door jamb. Unfortunately, there is almost no way to hide wires leading from wall switches or ceiling fixtures. Even running wires outside a wall requires cutting holes in the wall.
Turn off power to the electrical circuit you will be working on. Remove the skirting boards between the socket you're tapping for the electrical power and the new receptacle space. Be careful not to crack or break this trim, as you will be reinstalling it later.
Examine the plasterboard near the floor. Normally the plasterboard will end about 1.2 cm (1/2 inch) above the floor; you'll run the cable in this space. If the plasterboard extends all the way to the floor, you have to cut a channel along the bottom to contain the wire so the baseboard will be flush with the wall when it is reinstalled.
Take the cover off the receptacle and pull the socket from the electrical box. On the bottom of the box is a "knockout" that must be removed so the new electrical cable can be attached. If the knockout has not been removed, punch it out using a hammer and screwdriver. Cut a small notch at the base of the plasterboard to pull the BX cable through. Make sure this notch is not larger than the moulding.
Prepare the spot for new electrical box by first holding it against the wall and tracing its outline. Make sure the tracing is plumb before you begin cutting or the socket will be crooked. Cut the hole for the new socket and a notch similar to the one below the existing socket. Mount the electrical box to the wall according to the manufacturer's instructions.
Connect the BX cable to any unused power supply terminals on the source socket. Do not combine the new wires on the same terminals as the existing power supply wires. In this situation, create a "pigtail" by disconnecting the power supply line from the existing socket and attaching a new short wire to the socket terminals. Combine the power supply, the new short wire and the BX cable using a plastic connector.
Drop the BX cable down behind the wall and through the notch. Run it along the base of the plasterboard to the new receptacle. The cable can be carried around any door jambs if necessary by removing the door trim. Pull the BX cable through the notch at the new receptacle and up through the knockout. Attach the wires to the new receptacle and mount the receptacle in the box.
Replace the skirting, moulding and door trim, if necessary.
Because the nails holding the skirting boards in place can easily penetrate non-metallic sheathed cable, the best wiring material to use in this situation is flexible metal-sheathed cable, also known as BX cable.
Before beginning the project make sure that the electric cable is rated for the existing circuit, usually 230 volts and 15 or 20 amps.